Conventional ten speed bicycle transmissions consist of a chain wrapped around a front double sprocket and a rear cluster containing five sprockets, a front and rear derailleurs for derailing the chain from one sprocket to another in response to a rider moving two control levers which are connected to the derailleurs. The derailleurs are made of a large number of delicate parts which need frequent maintenance and adjustment, and are easily damaged. The derailleur system is also hard to operate, it generates continuous noise and inefficiencies in certain gears due to the chain's misalignment. To reduce the misalignment thin sprockets and a narrow chain are used. This narrow chain is also designed to withstand the repeated sharp double bend that is imposed by the rear derailleur's tensioner, and it is manufactured without a connecting link which would interfere with the adjacent sprockets and the tensioner's cage. Because of the popularity of the derailleur system this narrow chain is available throughout the industry and in every bicycle repair shop, and it is commercially advantageous to incorporate this chain in any new competing transmission system.
Due to the derailleur system deficiencies several attempts have been made in the past to introduce different systems, some of which are based on variable-sprockets. An example is found in British Pat. No. 453,712 by Neale which is incorporated by reference herein. However, this and other designs while being workable lacked the degree of refinement to be commercially successful especially in the area of synchronization of the sprocket-segment-planet with the chain. Under the stress of transmitting the rider's power to the wheel the variable-sprocket slightly deforms, interfering with the synchronization: therefore, it is best to arrange the engagement and disengagement of the sprocket-segment-planet and the chain to occur when the stresses and the accompanying deformations are at their lowest level.
An object of the present invention is to overcome these and other deficiencies of the prior art, and to provide a simple durable system which can be economically mass produced.